Although the M160 is great on electric guitars it's going to sound more scooped and brighter than the R121. I also found it more difficult to place. It's not like an R121 where you can just stick it dead center and have it sound great. I think it has a more focused sound than the R121, whereas the R121 sounds bigger and warmer.
Here's some stuff I recorded ages ago using M160's through Vintech 1272's on a Marshall JMP / 4x12 and a Marshall JCM200 / 4x12. In the mix I used the UAD Pultec EQ. Guitars were Les Paul and SG.
Funeral Diner the wicked - Download from http://www.selmatravels.de - Filestube.com
Brad